Still waiting for an answer on the serial number and the yoke markings.
T
Majspud the "Standard Catalog of S&W" has a general listing of serial numbers and their approximate shipping years although the only way to know for sure is with a factory letter or ship date from Roy Jinks if you become a SWCA member.
Fixed site K frames are not my focus but any K frame M&P with an "S" prefix or no prefix was made before the C prefix so C&R eligible,
IIRC if you stay under C 500,000 you should be ok,
The D prefix came after and then they went to the alphanumeric serials Like AAA 1234 etc
The upper sideplate screw is a dead giveaway on K and N frame S&W revolvers since it was deleted around 1955 giving you a 10 year safety window.
That being said the 4 screw S&W K and N frames change to the modern 3 screw style by around 1963 so getting tighter there just using the screw in the trigger guard.
If in doubt post pics and ask until you get the hang of it.
One more thing the Model stamping in the yoke begins around 1957 so if it is not model marked its usually going to be C&R eligible but always check the serial...
Here is a short list of K target serials but be advised the ship dates are not absolute just rough guesses.
K Series K Frames (Adjustable Sight Models)
K101 – K18,731…… 1947
K18,732 – K73,121… 1948
K73,122 – K84,149……1949 140 early 4" pre 18's shipped
K84,150 – K104,047….1950
K104,048 – K136,690...1951
K136,691 – K175,637...1952
K175,638 – K210,095...1953
K210,096 – K231,255...1954
K231,256 – K266,154...1955
K266,155 – K288,988...1956
K288,989 – K317,822...1957
K317,823 – K350,547...1958
K350,548 – K386,804...1959
K386,805 – K429,894...1960
K429,895 – K468,098...1961
K468,099 – K515,478...1962
K515,479 – K553,999....1963
K555,000 – K605.877....1964
K605,878 – K658.986....1965
K658,987 – K715,996....1966
K715,997 – K779.162....1967
K779,163 – K848,781....1968
K848,782 – K946,391....1969
K946,382 – K999,999....1970
Modern 3 screw frames the serial number is going to be the clue and my guess is if you stay under K 500,000 in K target frames you are ok, at K600,000 the safety window gets alot smaller .
PS I frames and J frames use a different system altogether.